Various attempts have been made to encapsulate and otherwise immobilize biological cells so that they remain viable and in a protected state within a semi-permeable membrane which permits the passage into the capsule of nutrients, oxygen and other species required for sustaining cell viability and metabolic functions and which also permits cell metabolites to pass out of the capsules.
In one prior art process, described in U.S. Pat. No. 4,251,387, capsules are manufactured by interfacial polymerization effected by reacting cationic monomers containing multifunctional amine groups with complementary anionic species. Polyelectric complex formation is accomplished by the formation of salt-bridges between anionic and cationic species.
Prior art immobilization procedures generally have suffered from one or more of the drawbacks of high material costs, high potential for contamination during the immobilization process, oxygen and nutrient limitations in the immobilized cell matrices, mechanical and/or chemical instability of the immobilized cell matrices, a narrow range of biocompatibility of matrix materials with cells and the use of expensive weighting materials.